(1) Field of the Invention
The present invention relates to a multiplex writing implement having two types of writing elements at least including a ball-point pen element filled up with so-called thixotropic water-soluble (medium viscosity) or low-viscosity oil-based ball-point pen ink, and any other combined one such as a normal oil-based ball-point pen element, mechanical pencil element, etc.
(2) Description of the Prior Art
There is a known writing implement called a multiplex writing implement, which has a plurality of writing elements such as a ball-point pen etc., and which selectively allows one of the elements to come in and out at the front end thereof.
Examples of the mechanisms for projecting and retracting writing tips in multiplex writing implements include a clicking type, a slider type in which sliders exposed to the outside from the side of the barrel cylinder of the writing implement should alternately be slid, a cam type in which a cam cylinder having a slope is rotated to achieve the function, etc.
Since the conventional projecting/retracting mechanisms incorporate return springs for retracting writing elements into the barrel cylinder, it has a complicated structure needing an increased number of parts and resulting in an increased cost.
Since the ink reservoir for a medium viscosity water-soluble or low-viscosity oil-based ball-point pen needs to be of a greater diameter, if it is mounted in a multiplex writing implement of a normal diameter, a sufficiently large margin between the writing elements can not be created and hence the tip parts of the writing elements to be projected can not be guided smoothly to the center of the tip opening of the barrel cylinder. The movement of the writing elements is impeded, and consequently, projection of the tip parts of the writing elements could be hindered. In order to enhance operation, the barrel cylinder should be made very much greater in its diameter, but this degrades its handling performance.
Conventional multiplex implements have a risk that ink will be sucked out and stain clothes if the writing implement is placed in a pocket etc. with its writing point projected out.
Since water-type ball-point pens use an ink which has a low viscosity of a few mPa.S or less, the ball-point pens of this kind offer an advantage that the user does not need to press hard and can write comfortably. Ball-point pens of this kind, however, suffer from some drawbacks, such as the forward leakage phenomenon, the back leakage phenomenon, etc. The former phenomenon causes the ink to ooze out from the writing point, whilst the latter phenomenon is caused by air entering the point assembly via the writing point, inducing the ink to flow out backwards. These phenomena can be prevented by using a piece of fabric called a `sliver`. On the other hand, if the ball-point pen is left with its cap off, the solvent tends to evaporate because of a high vapor pressure of the solvent. Therefore, there is a concern that the writing point might dry up, causing a lack of ink flow thereby prohibiting writing.
On the other hand, since conventionally known oil-based ball-point pens use an ink having a viscosity of some thousands of mPa.S or more, a considerably large friction arises when the ball rolls and the ink flows out from the writing point, resulting in an uncomfortable writing sensation. Further, at times an insufficient amount of ink flows from the writing point during writing and at others ink blobs, therefore lines drawn may be irregular in parts, the density of the written trace may be light, or a strong pressure for writing may be needed.
As an improvement of the oil-based ball-point pen, recently, a ball-point pen for water-soluble ink which has a viscosity half way between that of the above water-soluble type and the oil type (ranging from a few mPa-S to some thousands of mPa.S), has been developed. This ball-point pen uses water-soluble ink that presents a relatively low viscosity and has so-called thixotropy, which is the characteristic which lowers the viscosity of ink as the tip ball rolls during writing, thus allowing smooth distribution of ink. This type of ball-point pen, however, has the defect that the ink tends to dry up; therefore, it normally needs a cap which is able to seal off the writing tip. Additionally, since the amount of the ink flowing out will increase, it is also necessary to make the ink reservoir greater in diameter to store a larger quantity of ink, in order to increase its writing life.
As an improvement of the oil-based ball-point pen, it is possible to also consider a ball-point pen which uses an oil-based ink which has both a low viscosity and an excellent dryout-resistance. But a ball-point pen of this type, still has the problem that a large amount of ink flows out. Again, in this case, it is necessary to make the ink reservoir greater in diameter to store a greater quantity of ink, in order to increase its writing life. Moreover, since the viscosity of the ink is low, when the tip is placed down and a gap is created between the tip ball and the tip holding portion, ink oozes out (forward leakage) and an excessive amount of ink flows out during writing.
Since the water-soluble ink having a medium viscosity and the low-viscosity oil-based ink both have a relativity low viscosity, this tends to cause back leakage or forward leakage of ink. If the back or forward leakage of ink occurs, the ink may stain clothes etc. Further, another defect may occur in which, due to impacts from being dropped or clicking, ink-starving is likely to occur during writing. Further, the ball-point pen with a medium viscosity water-soluble ink usually has a translucent, nondrying greasy material called a `follower` added at the rear end of the ink reservoir. Therefore, when trying to prevent ink evaporation, it is adequate to consider the reduction of evaporation of ink from the point assembly, or the gap between the ball and its holder. Therefore, if, for example, a solvent having a considerably low vapor pressure is mainly used as in an oil-based ball-point pen, it is not necessary to consider the evaporation of ink. In the case of the water-soluble ink, however, the main component of the solvent is water; therefore even use of low vapor pressure solvents can not completely prevent water from evaporating.